1. Field of the Invention
The present invention provides a voltage regulator for a direct current (DC) power supply, and more particularly, a voltage regulator for stabilizing an output voltage of a fuel cell.
2. Description of the Prior Art
Please refer to FIG. 1. FIG. 1 is a conventional power supply system 100 for a portable electronic device. As shown in FIG. 1, the power supply system 100 is coupled to a portable electronic device 140. The power supply system 100 comprises an alternating current (AC) power source 120 and an AC/DC converter 110. The portable electronic device 140 comprises a conventional battery 130. The AC power source 120 is coupled to the AC/DC converter 110 for providing AC power to the AC/DC converter 110. The AC/DC converter 110 is coupled between the AC power source 120 and the conventional battery 130 for converting the received AC power to DC power and providing the DC power to the conventional battery 130 and the portable electronic device 140. Thus, the conventional battery 130 can be charged and the portable electronic device 140 can operate regularly.
When the AC power source 120 is not accessible, the AC/DC converter 110 cannot provide the DC power to the conventional battery 130 and the portable electronic device 140. Meanwhile, the portable electronic device 140 only operates by discharging the power stored in the conventional battery 130.
Generally, the ability of the conventional battery 130 to discharge has a ceiling. That is, the discharging period of the conventional battery 130 is limited. For example, the discharging period of a lithium cell for a notebook computer is about two hours. Therefore, when the portable electronic device 140 has to operate for more than two hours, the conventional battery 130 cannot provide enough power to the portable electronic device 140, which is a great inconvenience.